Dimethyl phthalate, diethyl phthalate, dibutyl phthalate and bis(2-ethylhexyl)-phthalate in aqueous solution were irradiated in the presence of TiO2 with wavelengths λ > 290 nm. Because of the attack of OH radicals generated by the UV irradiation of the semiconductor degradation of the phthalates is observed. Hydroxyphthalates and dihydroxyphthalates were determined as intermediate products of the photocatalytic reaction, which can be accelerated by the addition of oxygen.